A flavoprotein containing non-heme iron. The enzyme is capable of acting on a variety of nicotinate analogues to varying degrees, including pyrazine-2-carboxylate, pyrazine 2,3-dicarboxylate, trigonelline and 6-methylnicotinate. The enzyme from Clostridium barkeri also possesses a catalytically essential, labile selenium that can be removed by reaction with cyanide.